(a) Field of the invention
The present invention is related to radio receiver, and more particularly it pertains to an FM stereophonic receiver having a system for producing a test signal to be used for setting the input level of a tape-recorder recording an FM program through the receiver.
(B) Description of the prior art
When recording an FM program through an FM stereophonic receiver by a tape-recorder, it is important to properly set the input level of the tape-recorder because FM programs have considerably wide dynamic ranges. In case the tape-recorder has an excessive input level, the recorder signal of the FM program will contain amplitude distortions to a great extent. Conversely, if the input level is too low, the recorded signal will be accompanied by increased noises. In order to achieve an optimum condition, in general, the input level should be set so that the VU (recording input level) meter provided on the tape-recorder will indicate +3VU in case an FM broadcast signal of 100% modulation is received by the receiver through which the tape-recorder records an FM program.
An FM stereo tuner according to the prior art, however, is equipped with no system for producing a test signal intended to be used for input level setting of the tape-recorder. In the past, therefore, it has been necessary, for the accomplishment of the input level setting, to use an audio signal generator to produce therefrom a test signal having the same amplitude as the receiver output does when the receiver receives an FM broadcast signal of 100% modulation degree.